The invention relates to an opening roller for an open-end spinning arrangement having a mounting of needles or teeth provided on the circumferential surface, the circumferential surface and the mounting being provided with a metal carbide coating, to which another coating is applied.
It is known from German Patent Document DE-A 35 43 428 that relatively high stress occurs at the mounting in the case of opening rollers of the initially mentioned type, particularly if synthetic-fiber material must be processed. It is also known that, for this reason, a coating of the mounting and of the circumferential surface is carried out which form a protection against wear. It is also known that, although the previously known coatings result in an increased protection against wear, they have the disadvantage that they have a negative influence on the fiber material. In order to avoid damage to the fiber material, it is provided in the known construction that a synthetic material is embedded by means of a coating that follows the first coating. This synthetic material must not have any influence on the protection against wear but only has the purpose of providing the coating with a smooth surface. However, this construction was also not completely satisfactory in practice. Although it was found that the individual fibers proper are not damaged and shortened extensively, small particles are detached from the fibers during the processing, particularly of synthetic fibers. These particles appear as dust which is deposited in the spinning rotor. This dust will then relatively rapidly lead to a disadvantageous change of the spinning characteristics.
An object of the invention is to provide an opening roller of the initially mentioned type which has extensive protection against wear and also largely prevents the formation of fine dust.
This object is achieved according to the invention by providing that a thin nickel layer is provided over the metal carbide coating.
Surprisingly, it was found that by means of such a thin nickel layer over the metal carbide coating, the protection against wear is virtually not reduced, but that the dust formation is largely excluded. One reason is probably the fact that the nickel layer results in a smoothing of the surface so that the fiber material to be processed suffers no "rubbing-off" which would appear as dust. Although nickel per se is not very resistant to wear, it was found that the coating as a whole has a high resistance to wear. The possible reason may be that, after an initial wear of the outermost nickel layer, the metal carbide layer appears in the form of islands and then determines the overall resistance of the surface to wear. The two constituents of the coating therefore fulfill different functions, specifically a protection against wear by means of the metal carbide coating, on the one hand, and a careful treatment of the fibers by means of the nickel coating, on the other hand.
In a further development of the invention, a coating method is provided in which first the circumferential surface and the mounting are provided with a metal carbide coating by means of plasma spraying, and the metal carbide coating is subsequently chemically after-nickeled. It was found that metal carbides can be chemically after-nickeled.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.